The present invention relates to centrifuges and is directed more particularly to an improved apparatus for generating signals indicative of the actual speed and maximum safe speed of a centrifuge rotor.
In order to make it possible to perform a variety of different kinds of separations, many centrifuges are designed so that they can operate with any of a variety of different kinds and sizes of rotors. Because any rotor can fail catastrophically or even explode if it is used at a speed in excess of its maximum safe speed, it is important that such centrifuges be able to determine the maximum safe speed of a rotor without having to rely upon the attentiveness of its operator. As a result, such centrifuges are ordinarily equipped with circuits known as rotor identification circuits which are adapted to determine the identity and therefore the maximum safe speed of a rotor from markings such as optically coded bands that appear thereon. One circuit of this type which utilizes three optically coded bands and three photocell detectors is described in U.S. Pat. No. 3,746,247, issued in the name of Camilliere on July 17, 1973. Another circuit of this type which utilizes the arcuate length of a single coding band and one photocell detector is described in U.S. Pat. No. 3,982,162 issued in the name of Olliffe on Sept. 21, 1976.
Accurate control of the speed of a rotor also makes it important that a centrifuge include an accurate tachometer for generating a signal indicative of the actual speed of the rotor. Because of the extremely high speeds at which many centrifuges operate, this tachometer is usually one that has no direct mechanical connection to the rotor. Tachometers of this type may, for example, include an optical detector for detecting the passage of one or more speed control markings that appear on the bottom or periphery of the rotor. Because of their different function, such markings are separate from any rotor identification markings and are monitored by a separate photocell detector and a separate channel of the centrifuge electronics.
While tachometer and rotor identification circuits of the above types are adequate for many applications, they have certain deficiencies which limit the usefulness thereof. One of these is that the optical properties of the speed control and rotor identification markings can deteriorate with time as a result of the accumulation of dirt or of mechanical abrasion. This deterioration of the markings can in some cases result in an erroneous tachometer signal or even in an incorrect rotor identification. The latter errors, in turn, can result in faulty centrifuge separations or even in catastrophic rotor failures.
Another deficiency of circuits of the above type is that they require a multiplicity of different kinds of markings on the rotor, and a corresponding multiplicity of detectors for reading information therefrom. This multiplicity of markings and detectors is reflected by a corresponding multiplicity of channels in the electronics of the centrifuge. This duplication of markings, detectors and channels caused the tachometer and rotor identification circuits of centrifuges to be relatively complicated and expensive.